Apron drive for a manure spreader

ABSTRACT

A main drive for a manure spreader including a pair of sheaves adapted to be conveniently interchanged between an input shaft and a propeller or output shaft for maintaining a relatively constant output speed for two different input speeds from a tractor&#39;&#39;s PTO.

United States Patent 1191 Campbell et al. 1451 Mar. 27, 1973 [54] APRONDRIVE FOR A MANURE [56] I References Cited SPREADER UNITED STATESPATENTS [75] Inventors: Willis R. Campbell Leola Warren 2,804,308 8/1957Neighbour et al ..74/1 1 X Brackblu, 3,059,505 10/1962 Reicks ..74/11 x[73] Assignee: Sperry Rand Corporation, New Holland, p 1 PrimaryExaminer-Leonard H. Gerin Attorney-John C. Thompson, Joseph A. Brown and22 Filed: I Nov. 1, 1971 James J. Kennedy [2]] Appl. No.: 194,234

[ M81 RACT s2 U.S. c1 ..74/219, 74/1 1 A main drive for a manurespreader including a Pair 0f 51 1111. c1. ..F16h 7/02, Fl6h 37/00Sheaves adapted to be nvenienfly interchanged 58 Field of Search..74/11, 219, 217 R between an input Shaft and a pmpellef outPut Shaftfor maintaining a relatively constant output speed for two difierentinput speeds from a tractors PTO.

14 Claims, 12 Drawing Figures PATUJHTRHmz 7 m3 SHEET 10F 3 INVENTOR. IW/LL/S R OQMPBELL WQFEEN BRQCKB/LL BY ATTORNEY BRIEF DESCRIPTIOn OF THEDRAWINGS FIG. 1 is a diagrammatic foreshortened side elevational view ofa manure spreader wagon body illustrating drive mechanism constructed inaccordance with the invention applied thereto;

FIG. 2 is a fragmentary end view, on a somewhat enlarged scale, asviewed from the left in FIG. 1;

FIG. 3 is a cross section taken approximately on the irregular line 3--3of FIG. 2 with the belt tightener pulley of FIG. 2 omitted and with thewagon body shown in elevation; 7

FIG. 4 is a face view of the propeller shaft sheave as viewed from theleft in FIG. 3;

FIG. 5 is a face view of the pto shaft sheave as viewed from the left inFIG. 3;

FIG. 6 is an exploded view of the sheave and associated parts of FIG. 4;

FIG. 7 is an exploded view of the sheave and associated parts of FIG. 5;

FIG. 8 is a detail view of the hub member of the sheave of FIG. 4;

FIG. 9 is a detail view of the hub portion of the sheave of FIG. 4;

FIG. 10 is a detail view of the hub member of the sheave of FIG. 5; and

FIG. 11 is adetail view of the hub portion of the sheave of FIG. 5;

FIG. 12 is a diagrammatic view illustrating an interchange of thesheaves of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to thedrawings the load carrying wagon body of the manure spreader illustratedis of well known form and comprises in general side walls 15, a frontwall 16, a'floor 17 and an open rear at which a beater unit 18 islocated. Extending along the floor from front to rear is an apronconveyor 19 having slats 20 for advancing manure from the front of thewagon to the rear thereof for scattering by the scattering blades 21 ofthe beater unit 18.

Suitable drive mechanism is provided for the beater unit 18 which inthis instance includes a right angle gear unit 22, an output orpropeller shaft 23 connected to the input shaft 24 of the gear unit 22,and a clutch 25 controlling the input shaft 24. Suitable drive mechanismis also provided for the apron conveyor 19 which in this instanceincludes a lay shaft 26, constituting the input shaft of a worm gearunit 27, drivingly connected to the propeller shaft 23 by sprocket andchain drives 28 and 29 adapted to be selectively connected to the inputshaft 26 by the clutch 25. The output shaft 30 of the worm gear unit 27is drivingly connected to the drive shaft 31 of the apron conveyor 19 bymeans of sprockets 32 and 33 and drive chain 34. The clutch 25 isadapted to be controlled by a clutch actuator 35 and yoke 36 which isactuated by means of a quadrant control lever 37 having a pawl 38 (FIGS.1 and 2) operating in notches 39 of a quadrant 40.

The quadrant control lever 37 and the manner in which it controls thebeater unit 18 and apron conveyor 19 form no part of the presentinvention, per se, and therefore detailed description thereof is notnecessary. It is also pointed out that other known forms of beater andapron conveyor drives may be employed without departing from the scopeof the present invention.

The present invention is primarily concerned with the main drivemechanism 45 from the pto shaft of an associated tractor to theaforesaid propeller shaft 23 and to the adaptability of this drivemechanism for use with tractors, having for example rpms of say either540 and 1000 rpm. The invention contemplates, by simple and efiectivemeans, the driving of the apron conveyor and beater unit at the samepre-determined speeds whether a tractor having a standard 540 rpm inputor a tractor having a standard 1000 rpm input is employed to operate themanure spreader.

Referring now to FIGS. 2 and 3 it will be seen that a large diametersheave 46 is secured on the propeller shaft 23 and that a smallerdiameter sheave 47 is secured on the lower shaft 48. The lower shaft 48is connected to the pto shaft of the tractor (not shown) in knownmanner. A drive belt 49 connects the sheaves 46 and 47.

The sheave 46 is mounted on the propeller shaft 23 by means of a hubmember 50. The hub member 50 is keyed to the propeller shaft 23 by a key51 and firmly secured in place by a set screw 52. The hub member has aflange 53 to which the sheave is secured by means of a shear bolt 54. Asnap ring 55 laterally positions the sheave on the hub member. In theevent that any jam conditions occur in the beater or apron conveyordrive areas the shear bolt will shear to prevent damage to themechanism. As seen in FIG. 3 the bore of the sheave is provided with abearing sleeve 56 for free rotation of the sheave when shear occurs.

Similarly the smaller sheave 47 is mounted on the lower shaft 48 bymeans of a hub member 60 which is keyed to the shaft 48 by a key 61 andfirmly secured in place by a set screw 62. The hub member 60 has aflange 63 having three equally radially spaced holes 64 registering withthree similar holes 65 in the sheave 47 for the reception of securingbolts 66.

An important feature of the present invention resides in the simplemanner in which the sheaves 46 and 47 can be interchanged to suit thetwo driver speeds of 540 and 1000 rpm mentioned above. The sheaves 46and 47 arranged as shown in FIGS. 2 and 3 are for 1000 rpm, i.e., thesmaller sheave 47 is the driver rotating at 1000 rpm.

When the lower shaft 48 is being rotated at 540 rpm the larger sheave 46is secured on the shaft 48 andthe smaller sheave 47 is secured on ehtshaft 48 and the smaller sheave 47 is secured on the propeller shaft 23(FIG. 12). As shown in the exploded view of FIG. 6 in order to removethe large sheave 46 from the propeller shaft the snap ring 55 is removedfrom the hub member 50, the shear bolt 54 is removed, the set screw 52is loosened and the hub member is removed from the sheave.

As shown in the exploded view of FIG. 7, in order to remove the smallshave 47 from the shaft 48 the three bolts 66 are removed and shaft 48and its hub member 60 are withdrawn from the sheave 47. Then the sheave47 is slipped onto the hub member 50, the snap ring 55 is inserted, theshear bolt 54 is secured in place, and finally this assembly is slippedonto the propeller shaft 23 and the set screw 52 is tightened, then thelarge sleeve 46 is aligned onto the hub member 60 and the three securingbolts 66 tightened to secure the sheave in place. This interchange ofpulleys is diagrammatically shown in FIG. 12.

1 APRON DRIVE FOR A MANURE SPREADER BACKGROUND OF THE INVENTION Thepresent invention relates to manure Spreaders and the like, and moreparticularly to a drive system therefore.

In the past, most tractors, particularly the type adapted to be used inconjunction with agricultural implements, have been provided with a 540rpm pto drive. But in the last years, tractor manufacturers have beenincreasing both the size and the horsepower of the tractors beingproduced. With this growth in size of tractors has come a new ptosystem, namely a system with a 1000 rpm output rating. The situation ofhaving tractors with rated outputs of both 540 rpm and 1000 rpm hascreated a delimina for the agriculture engineer, because he is not awareof what particular type of tractor the farmer who purchases theimplement he is designing will employ. Consequently, the engineer doesnot know what type of drive to design for a particular implement. In themanure spreader for example, the engineer must design the drive suchthat the spreading mechanismand apron drive function in-an efficientmanner. The same principle is equally applicable to other tractor drawnimplements as well, since the drive therefore normally dictates therelative speeds of the implements working elements.

In light of the foregoing remarks it is apparent that some type ofdevice is needed to adapt a particular implement to a tractor havingeither 1000 or 540 rpm pto systems. One form of solution that has beengiven some attention concerns the use of a gearbox to step-up orstep-down an input speed. For example, one is directed to US. Pat. No.3,059,505 to L. J. Reicks which discloses a portable speed adapter forthe power takeoff of a tractor. In this particular disclosure, Reicks,like others, has suggested the use of a gearbox to reduce or step-up theinput from the tractor as may be desired by the farmer relative to anagricultural implement that is to be employed in conjunction with thetractor. But it is clear that the addition of a gearbox to reduce andstepup the input speed in a very costly addition, besides sometimesbeing quite awkward to adapt between the tractor and the particularagricultural implement being drawn thereby.

7 SUMMARY OF THE INVENTION In view of the foregoing remarks, applicantshave designed a drive system for a manure spreader that includes a pairof interchangeable sheaves that may be a relatively constant output seedto the various power consuming mechanisms of the particular agriculturalimplement. I

Another object of the present invention resides in the provision ofinterchangeable drive elements within the main drive of an agriculturalimplement, the drive elements being adapted to be selectivelyinterchanged in response to a change between two input speeds tomaintain a relative constant output speed for either of the two inputspeeds.

More particularly, it is the object of the present invention to providethe main drive of an agricultural implement with drive elements in theform of a pair of drivingly interconnected sheaves, wherein the radiusof one sheave is less than the radius of the other sheave such that thesheaves may be selectively interchanged as two different input speedsare interchanged to maintain a relatively constant output speed.

A further object of the present invention resides in the provision of amain drive for an agricultural implement including a pair of differentsized interchangeable sheaves, the ratio of the radii of the two sheavesbeing selectively interchanged relative to the particular tractor ptospeed to yield a generally constant output speed, thereby providing arelatively constant input speeds to the working components of the manurespreader, namely the spreading mechanism andv the apron drive. Moreparticularly, the present pair of interchangeable sheaves includes asmaller sheave and a larger sheave with the radii of each yielding aparticular ratio relative to two input speeds, a low and high inputspeed, such that the resultant output speed remains nearly constantirrespective of the particular input speed applied.

It is therefore the principle object of the present invention to providean agricultural implement having a main drive that is adaptable toreceive two substantially different input speeds and yet, in eithercase, maintain preselected such that by interchanging the two sheavesrelative to either of two input speeds an output speed that falls withina range of values generally midway between the values of the two inputspeeds is maintained.

, More particularly, it is the object of the present invention toprovide a pair of interchangeable sheaves, one sheave being smaller thanthe other, with the ratio of the smaller sheaves radius to the largersheaves radius being approximately equal to the square root of the valueof a high input speed divided by a low input speed. I

Another object of the present invention resides in the provision ofdetachable securing means associated with each said sheaves, wherebythey maybe quickly and easily attached and detached from the main drive.

Another particular object of the present invention resides in theprovision of a main drive for a manure spreader that is adapted to bepulled behind and powered by a tractor having a PTO speed of either 540rpm or 1000 rpm, the main drive of the present manure spreader includinga pair of interchangeable sheaves each adapted to be selectively mountedon one of a pair of drive shafts, the drive shafts being termed an inputdrive shaft and a propeller or output drive shaft, the pair of sheaveshaving radii particularly selected relative to each other to yield aratio that enable the main drive to yield a relatively constant outputspeed for either input speeds of 540 or 1000 rpm, the relativelyconstant output speed being achieved by selectively interchanging thepair of sheaves in response to a change in the input rpm speed such.that the smaller sheave is fixed on the input shaft when the smaller rpminput of 540 rpm is being used, and wherein the larger sheave is placedon the input shaft when the larger input rpm speed 1000 rpm is employed.

In regard to the aboveobject, it is a particular object of the presentinvention to provide the above pair of sheaves with a particular radii,the particular radii being such that the ratio of the smaller radii tothe larger radii equals approximately the square root of 1000 rpmdivided by 540 rpm or approximately 1.36, thereby yielding a relativelyconstant output speed of approximately 735 rpm.

In connection with this interchange of sheaves it will be observed thatthe large sheave 46 has three bolt holes 70 and a shear bolt hole 71(FIG. 9) and similarly the small sheave 47 has three bolt holes 65 and ashear bolt hole 72 (FIG. 11). The hub member 50 only has a shear bolthole 73 (FIG. 8) and the hub member 60 only has three bolt holes 64(FIG. It is noted that the three holes in the sheaves are located on aradius R which is larger than the radius R on which the shear bolt holeis located. This arrangement avoids putting a shear bolt in any of thethree securing bolt holes.

Referring to FIG. 2 it is pointed out that the drive system is protectedagainst overload by a spring loaded idler pulley 75 which allowsfor-controlled slip during initial start up and acts as a cushion forpeak torques.

The real essence of the present invention lies in the provision of amanure spreader drive system that yields a constant output speed for twodifferent input speeds. This is accomplished by providing a pair ofsheaves 46,47 with radii of a preselected ratio relative to the twoinput speeds to be'employed by the spreader drive system. Once theoperator changes from one input speed to another, the same output speedor nearly the same may be maintained by simply interchanging the twosheaves 46,47.

For purposes of explanation let, us refer to the radii of the smallsheave 46 as R the radii of the larger sheave 47 as R the two inputspeeds as low input speed 5,, and high input speed S and since aconstant output speed is always desired this will be referred to by theletter K. It is well known that in the case of two successively drivensheaves or pulleys the radius of one is inversely proportional to thespeed of the other. Moreover, to obtain a constant output speed, whichmust be between 8,, andS the larger sheave 46 will be used as the inputsheave when the low input speed 5,, is employed and the smaller sheave47 will be used as the input sheave when the high input speed isemployed. Therefore for the two different situations we can write thefollowing two equations:

RS/RL K/SL L/ s u Solving each equation for K yields the following:

K 1. SH/RS Since the output speed K is constant for either input speed Sor S one can set the right sides of the above equations equal to eachother and solve for the ratio R /R as follows:

s 81., 1. RL SH/RS sheaves 46,47 when the input speed is changed suchthat when 540 rpm is used as an input, the larger sheave 46 turns withthe input shaft and the smaller sheave 47 is fixed to the output orpropeller shaft 23, and visa versa when the high input speed of i000 rpmis used.

It follows that for any two given input speeds S S a constant outputspeed can be maintained for either input speed by substituting thevalues of S and S in equation 7 above and solving for the ratio R /Rwhich, as previously pointed out, is the ratio of the radius of onesheave to the radius of another sheave.

As is apparent from the foregoing, a ratio of R; to S,, can bedetermined which will yield an almost exact constant output speed foreither input of 8,, or S But in practice, one, of course, findsvariables within the drive system which tends to make a desire forexactness meaningless. For example, the input speeds of 540 and 1000 rpmvary with the throttling of the tractor. Therefore, it is obvious thatthe output speed will most often fall within a range of values, therange being a function of the input speeds and various step-ups andreductions in the entire main drive. Since in the present case, the pairof interchangeable sheaves 46,47 make up the drive, the range of outputspeeds will necessarily fall within the range between 540 and 1000 rpm.

The terms, upper, lower, forward, rearward etc, have been used hereinmerely for the convenience of the foregoing specification and in theappended claims to describe the main drive for a manure spreader and itsparts as oriented in the drawings. It is to be understood, however, thatthese terms are in no way limiting to the invention since the main drivefor a manure spreader may obviously be disposed in many differentpositions when in actual use.

The present invention, of course, may be carried out in other specificways than those herein set forth without departing from the spirit andessential characteristics of the invention. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive, and all changes coming within the meaning and equivalencyrange are intended to be embraced herein.

Having thus described our invention, what we claim 1. In a manurespreader of the type adapted to be pulled behind a tractor and having awagon type body structure, a manure spreading mechanism disposedtransversely the rear of the wagon body structure, an

pto drive having either a low input speed 8,, or a high input speed S b.a propeller shaft rotatively mounted to said manure spreader and havingone end operatively connected to said means for driving said manurespreading mechanism and said apron drive;

c. a pair of interchangeable sheaves each detachably mounted to eitherof said input or propeller shafts such that they may be interchanged.therebetween, said pair of sheaves including a small sheave having aradius R and a larger sheave having a radius R the ratio R; to R or viceversa being preselected relative to the two input speeds S and 8,, suchthat a relatively constant propeller shaft speed can be maintained byinterchanging said sheaves between said shafts such that when the lowinput speed 8,, is drivingly connected to the input shaft the smallsheave with radii R; will be mounted on said input shaft and the largersheave with radii R will be mounted on the propeller shaft, and when thehigh input speed S is drivingly connected to said input shaft thesheaves are interchanged such that the larger sheave with radii R ismounted on the input shaft and the smaller sheave with the radii R; ismounted on the propeller shaft to -yield a propeller shaft speedcomparable to that when the sheaves were reversed on the respectiveshafts; and

propeller shaft speed the ratio 4. A main drive for a manure spreader asrecited in claim 3 wherein thelow input speed 8,, is 540 rpm and thehigh input speed 8,, is 1000 rpm, thereby yielding a value for the ratioR; to R of approximately 1.36.

5. In a manure spreader having a wagon type body structure, a spreadingmechanism disposed transversely the rear thereof, and apron conveyordisposed within the body structure for conveying manure rearwardly tothe spreading mechanism, and a main drive associated with said manurespreader for driving said spreading mechanism and said apron drivecomprising:

a. an input drive shaft having one end rotatively mounted within saidmanure spreader and the other end adapted to be connected to a tractorpower take-off drive having either a low input speed 8;, or a high inputspeed S b. a propeller shaft rotatively mounted to said manure spreaderand having one end operatively connected to said spreading mechanism andsaid apron drive for driving both;

0. a pair of interchangeable sheaves each being provided with detachablesecuring means and adapted to be secured to either of said shafts, saidinterchangeable sheaves being particularly sized with the radius of onebeing smaller than the radius of the other such that by selectivelyinterchanging the sheaves relative to the particular input speed beingemployed results in a propeller shaft speed that falls within a range ofmedium values between S and S,,, the selective interchanging of said adrive belt drivingly interconnected between said sheaves entailing themaintenance of the smaller radius sheave on said input shaft when 8,, isdrivingly connected thereto and the interchanging of said sheaves suchthat the larger radius sheave is mounted on the input shaft when S isemployed; and

. a belt drive drivingly interconnecting the sheaves such that thetorque imparted to the input shaft is transferred to the propeller shaftwith the speed of the propeller shaft being maintained within the mediumrange of speeds defined in paragraph c above.

6. A main drive for a manure spreader, as recited in claim 5, whereinsaid detachable securing means includes a hub member and means forsecuring said hub member to a respective shaft and means for securingeither of said sheaves to said hub members.

7. A main drive system for an agricultural implement adapted to becoupled to and powered by a tractor, comprising in combination: anagricultural implement having a power consuming mechanism associatedtherewith; an input drive shaft carried by said agricultural implementand adapted to be connected to a pto drive extending from said tractorand having either a low input speed or a high input speed; an outputdrive shaft mounted to said agricultural implement and operativelyconnected to said power consuming mechanism for driving the same; adrive interconnecting said input shaft with said output shaft fortransferring the torque delivered to said input shaft by said tractorpto to said output shaft, said drive including a pair of interchangeabledrive elements adapted to be selectively interchanged within said drivefor maintaining a relatively constant output speed for either of saidlow or high pto input speeds.

8. A main drive for an agricultural implement, as recited in claim 7,wherein each of said drive elements are provided with detachablesecuring means for securing each drive element to either said input oroutput Q shafts.

9. A main drive, as recited in claim 7, wherein said drive elements aredisposed adjacent each other and are provided with interconnecting meansfor transferring the torque of one directly to the other.

10. A main drive system for an agricultural implement, as recited inclaim 9, wherein said means interconnecting said drive elements includesan endless flexible driving member trained around both driving elementsfor conveying the torque delivered to one to the other.

11. A main drive system for an agricultural implement, as recited inclaim 10, wherein said drive elements includes a pair of interchangeablesheaves with each sheave being provided with detachable securing meanssuch that each sheave may be selectively attached to either said inputor output shafts.

12. A main drive system for an agricultural implement, as recited inclaim 1 1, wherein an endless flexible drive belt is trained around saidsheaves for transferring the torque of one sheave to the other sheave.

13. A main drive system for an agricultural implement, as recited inclaim 12, wherein one sheave is smaller than the other sheave andwherein the ratio of the radius of the smaller sheave to the radius ofthe larger sheave is preselected relative to the values of the low andhigh pto input speeds.

1. In a manure spreader of the type adapted to be pulled behind a tractor and having a wagon type body structure, a manure spreading mechanism disposed transvErsely the rear of the wagon body structure, an apron conveyor disposed within the body for conveying manure rearwardly to the spreading mechanism, and a main drive associated with said manure spreader interconnecting a pto drive of the tractor and means for driving said manure spreading mechanism and apron conveyor, said main drive comprising: a. an input drive shaft having one end rotatably mounted to a forward portion of said wagon and the other end extending forwardly therefrom and adapted to be operatively connected to a tractor pto drive having either a low input speed SL or a high input speed SH; b. a propeller shaft rotatively mounted to said manure spreader and having one end operatively connected to said means for driving said manure spreading mechanism and said apron drive; c. a pair of interchangeable sheaves each detachably mounted to either of said input or propeller shafts such that they may be interchanged therebetween, said pair of sheaves including a small sheave having a radius RS and a larger sheave having a radius RL, the ratio RS to RL or vice versa being preselected relative to the two input speeds SL and SH such that a relatively constant propeller shaft speed can be maintained by interchanging said sheaves between said shafts such that when the low input speed SL is drivingly connected to the input shaft the small sheave with radii RS will be mounted on said input shaft and the larger sheave with radii RL will be mounted on the propeller shaft, and when the high input speed SH is drivingly connected to said input shaft the sheaves are interchanged such that the larger sheave with radii RL is mounted on the input shaft and the smaller sheave with the radii RS is mounted on the propeller shaft to yield a propeller shaft speed comparable to that when the sheaves were reversed on the respective shafts; and d. a drive belt drivingly interconnected between said sheaves for conveying the torque from said input shaft to said propeller shaft.
 2. A main drive for a manure spreader, as recited in claim 1, wherein each shaft is provided with a detachable hub member which includes means for fixing the hub member to a respective shaft and means for fixing either of said sheaves thereto.
 3. A main drive for a manure spreader, as recited in claim 1, wherein to maintain a relatively constant propeller shaft speed the ratio RS/RL about Square Root SH/SL.
 4. A main drive for a manure spreader as recited in claim 3 wherein the low input speed SL is 540 rpm and the high input speed SH is 1000 rpm, thereby yielding a value for the ratio RS to RL of approximately 1.36.
 5. In a manure spreader having a wagon type body structure, a spreading mechanism disposed transversely the rear thereof, and apron conveyor disposed within the body structure for conveying manure rearwardly to the spreading mechanism, and a main drive associated with said manure spreader for driving said spreading mechanism and said apron drive comprising: a. an input drive shaft having one end rotatively mounted within said manure spreader and the other end adapted to be connected to a tractor power take-off drive having either a low input speed SL or a high input speed SH; b. a propeller shaft rotatively mounted to said manure spreader and having one end operatively connected to said spreading mechanism and said apron drive for driving both; c. a pair of interchangeable sheaves each being provided with detachable securing means and adapted to be secured to either of said shafts, said interchangeable sheaves being particularly sized with the radius of one being smaller than the radius of the other such that by selectively interchanging the sheaves relative to the particular input speed being employed results in a propeller shaft speed that falls withiN a range of medium values between SH and SL, the selective interchanging of said sheaves entailing the maintenance of the smaller radius sheave on said input shaft when SL is drivingly connected thereto and the interchanging of said sheaves such that the larger radius sheave is mounted on the input shaft when SH is employed; and d. a belt drive drivingly interconnecting the sheaves such that the torque imparted to the input shaft is transferred to the propeller shaft with the speed of the propeller shaft being maintained within the medium range of speeds defined in paragraph c above.
 6. A main drive for a manure spreader, as recited in claim 5, wherein said detachable securing means includes a hub member and means for securing said hub member to a respective shaft and means for securing either of said sheaves to said hub members.
 7. A main drive system for an agricultural implement adapted to be coupled to and powered by a tractor, comprising in combination: an agricultural implement having a power consuming mechanism associated therewith; an input drive shaft carried by said agricultural implement and adapted to be connected to a pto drive extending from said tractor and having either a low input speed or a high input speed; an output drive shaft mounted to said agricultural implement and operatively connected to said power consuming mechanism for driving the same; a drive interconnecting said input shaft with said output shaft for transferring the torque delivered to said input shaft by said tractor pto to said output shaft, said drive including a pair of interchangeable drive elements adapted to be selectively interchanged within said drive for maintaining a relatively constant output speed for either of said low or high pto input speeds.
 8. A main drive for an agricultural implement, as recited in claim 7, wherein each of said drive elements are provided with detachable securing means for securing each drive element to either said input or output shafts.
 9. A main drive, as recited in claim 7, wherein said drive elements are disposed adjacent each other and are provided with interconnecting means for transferring the torque of one directly to the other.
 10. A main drive system for an agricultural implement, as recited in claim 9, wherein said means interconnecting said drive elements includes an endless flexible driving member trained around both driving elements for conveying the torque delivered to one to the other.
 11. A main drive system for an agricultural implement, as recited in claim 10, wherein said drive elements includes a pair of interchangeable sheaves with each sheave being provided with detachable securing means such that each sheave may be selectively attached to either said input or output shafts.
 12. A main drive system for an agricultural implement, as recited in claim 11, wherein an endless flexible drive belt is trained around said sheaves for transferring the torque of one sheave to the other sheave.
 13. A main drive system for an agricultural implement, as recited in claim 12, wherein one sheave is smaller than the other sheave and wherein the ratio of the radius of the smaller sheave to the radius of the larger sheave is preselected relative to the values of the low and high pto input speeds.
 14. A main drive system for an agricultural implement, as recited in claim 13, wherein the ratio of the radius of the smaller sheave to the radius of the larger sheave equals approximately the square root of the high input speed divided by the low input speed. 